This invention relates to procedures for detecting and identifying sulfate-reducing bacteria, or SRBs, and more particularly, to the use of oligonucleotide probes complementary to portions of the 16S rRNA molecule of these bacteria to detect and identify sporing and non-sporing sulfate-reducing bacteria.
Sulfate-reducing bacteria, such as members of the genera Desulfovibrio and Desulfotomaculum, reduce sulfate and/or sulfite under suitable anaerobic conditions, which leads to corrosion of iron-containing materials with which the bacteria are in contact, for example metal structures and conduits, and generate hydrogen sulfide, an odiferous, poisonous gas. Sulfate- reducing bacteria are also present in other systems, for example Desulfotomaculum ruminis is present in the rumen of ruminant animals, particularly cattle.
The presence of sulfate-reducing bacteria in many environments is undesirable, particularly in concentrations sufficient to cause significant corrosion of iron-containing metals in contact with SRB-containing aqueous solutions including fresh and sea waters. It is common practice to control SRB growth by adding an antimicrobial composition to the aqueous solutions containing them. However, antimicrobials are costly and therefore must be applied judiciously. Monitoring of the system to detect population density changes is a common practice, and antimicrobials are added either continuously or after the population density reaches certain levels.
In addition to causing corrosion of iron-containing metals, sulfate-reducing bacteria are largely responsible for generating hydrogen sulfide gas, a foul-smelling gas which is toxic at very low concentrations. SRBs are often present in a producing oil well which over a period of time "sours" and produces hydrogen sulfide gas which lowers the value of the oil. The presence of hydrogen sulfide in crude oil requires the use of precautions and protective measures for possible worker exposure to hydrogen sulfide gas thus the rapid identification and quantitation of SRBs is important to occupational safety.
In contrast to their undesired presence, SRBs are also present in the gut of ruminant animals, particularly domestic animals (cattle) used as protein sources for human consumption. Prepared animal feeds customarily contain antibiotics added as a prophylactic to prevent animal infections especially when the animal is moved from one feeding location to another. These feed additive antibiotics, sometimes called pro-biotics, may upset the animal's natural intestinal flora, which includes sulfate-reducing bacteria. A means to assess and monitor these bacteria and compare them to the pro-biotic selection and ingestion is also desirable. The above are but two illustrations of the applicability of the procedures of this invention and are not intended to be limiting.
By "sulfate-reducing bacteria" we mean bacteria capable of reducing sulfate to sulfite and/or sulfite to sulfide regardless of the taxonomic group of the bacteria.
Sulfate-reducing bacteria are a major source of corrosion in oilfield production waters, thus it is necessary to reduce their presence. A biocide may be used to control the growth of sulfate-reducing bacteria. Commonly, biocide is added to the water when the bacterial cell density exceeds a predetermined level, or biocide may be injected continuously. The current method of detecting the SRB cell level is by serial dilution in culture medium to detect cell growth, in which water samples are serially diluted into nutrient SRB medium and FeS production is observed by the formation of black precipitate. Commonly known as the American Petroleum Institute (API) method, obtaining results from this serial dilution assay may take as long as three to four weeks.